The present invention relates to a mattress for use on a bed and settee.
Mattresses for use on beds and settees comprise a flat spring unit including a plurality of compression coil springs arranged side by side. A cushion made of foamed synthetic resin material such as polyurethane and urethane foams is arranged on at least one of upper and lower sides of the spring unit with a protection layer interposed between them. The protection layer serves to keep the hard metallic spring unit from touching the soft cushion so as to protect the cushion from being broken. These components are covered by an outer covering. A mattress having an arrangement like this must keep its effective useful area large by making its circumferential portion have the same rigidity as its center portion. The circumferential portion of the mattress is given the desired rigidity by arranging reinforcing members at the circumference of the spring unit and connecting the reinforcing members to the coil springs located at the circumference of the spring unit by clips. Load applied to the mattress when the user lies on the mattress is transmitted and distributed to the coil springs through the reinforcing members as well. Therefore, the reinforcing members make the circumference of the mattress hard and distribute the load as well. Urethane foam rods, steel wire frames and metal strips having a V-shaped section are employed as the reinforcing members. The protection layer for separating the spring unit from the cushion serves to assist the cushion in attaining its predetermined flexure curve, thus giving a feeling of appropriate hardness to the user. It is believed that the reinforcing members and protection layer are indispensable to the mattress.
The protection layer is usually made of sisal or cotton. When the mattress is used for a long time and subjected to loads repeatedly, the protection layer is likely to become permanently deformed. The correct flexure curve of the cushion is deflected, creating local hardness and discomfort. Protection layers made of steel wires are also used to prevent the permanent deformation thereof. However, the metallic protection layer is liable to break the cushion. Japanese Utility Model Publication Nos. 47-39607 (published on Nov. 30, 1972 with Nippon Bed Manufacturing K.K. as its applicant) and 54-9456 (published on May 2, 1979 with Izumi Manufacturing Corporation as its applicant) disclose net-like protection layers made of synthetic resin to eliminate the above-mentioned drawback. Net-like protection layers made of synthetic resin are the least likely to deform permanently and to break the cushion.
With conventional mattresses, the protection layers are usually connected to the reinforcing members by clips and thus prevented from shifting on the spring unit. However, clips are likely to break the outer covering and cushion because they partially project outward.
Conventional mattresses employ reinforcing members to give desired rigidity to the circumference thereof, as described above. In addition, the reinforcing members, spring unit and protection layers must be connected to one another by clips which creates the possibility that the outer covering and cushion may break. These reinforcing members and clips also make the mattress assembly inefficient.